1. Technical Field
The present invention generally relates to a method for predicting sediment content of a hydroprocessed hydrocarbon product.
2. Description of the Related Art
Presently, the petroleum industry relies more heavily on relatively high boiling feedstocks derived from materials such as coal, tar sands, oil-shale, and heavy crudes. These feedstocks generally contain significantly more undesirable components, especially from an environmental point of view. For example, such undesirable components include halides, metals and heteroatoms such as sulfur, nitrogen, and oxygen. Furthermore, specifications for fuels, lubricants, and chemical products, with respect to such undesirable components, are continually becoming stricter. Consequently, such feedstocks and product streams require more severe upgrading in order to reduce the content of such undesirable components. More severe upgrading, of course, adds considerably to the expense of processing these petroleum streams.
Hydroprocessing, which includes by way of example, hydroconversion, hydrocracking, hydrotreating, hydrogenation, hydrofinishing and hydroisomerization, plays an important role in upgrading petroleum feedstocks to meet the more stringent quality requirements. For example, there is an increasing demand for improved hetero-atom removal, aromatic saturation, and boiling point reduction as well as removal of metal contaminants such as vanadium and nickel. Much work is presently being done in hydrotreating because of greater demands for the removal of undesirable components such as heteroatoms, most notably sulfur, from transportation and heating fuel streams. Hydrotreating is well known in the art and usually involves treating the petroleum streams with hydrogen in the presence of a supported catalyst at hydrotreating conditions.
Hydrocarbon feedstocks likewise generally contain polar core materials, such as asphaltenes, dispersed in lower polarity solvent(s). Intermediate polarity material(s), usually referred to as resin(s), can associate with the polar core materials to maintain a homogeneous mixture of the components.
Asphaltenes are organic heterocyclic macromolecules which occur in crude oils. Under normal reservoir conditions, asphaltenes are usually stabilized in the crude oil by maltenes and resins that are chemically compatible with asphaltenes, but that have lower molecular weight. Polar regions of the maltenes and resins surround the asphaltene while non-polar regions are attracted to the oil phase. However, changes in pressure, temperature or concentration of the crude oil can alter the stability of the dispersion and increase the tendency of the asphaltenes to agglomerate into larger particles. As these asphaltene agglomerates grow, so does their tendency to precipitate out of solution.
One of the problems encountered during hydroprocessing (i.e., refining) is sediment formation. The formation of sediments is related to the asphaltene content in the residue. Sediment formed during hydroprocessing operations may settle and deposit in such apparatuses as the catalytic reactor, distillation units and heat exchangers in the fractionation section. This affects the overall economy of the system since the reactor system cannot reach higher conversions. The prevention or suppression of these coke-like sediment materials is therefore highly desirable. Presently, there are only a few ways to determine sediment forming tendencies, and they are time-consuming and have a low repeatability. For example, ASTM test method 4870 is used for the determination of total sediment in residual fuels. This test method is time consuming, has several sources of errors and requires constant operator's attention. It also has a limited application to those residues that can be filtered under the conditions of the method. However, the data obtained from this test method is used for making decisions about operation conditions, activity and life of the catalyst, use of additive, etc.
Accordingly, it would be advantageous to characterize a hydrocarbon-containing feedstock prior to subjecting it to hydroprocessing in order to evaluate its propensity for sediment production following hydroprocessing. Thus, it would be desirable to provide methods for predicting sediment content of a hydroprocessed hydrocarbon product that can be carried out in a simple, cost efficient and repeatable manner.